Magnetorheological fluids with a molybdenum-amine complex

Abstract

One embodiment of the invention includes an MR fluid of improved durability. The MR fluid is particularly useful in devices that subject the fluid to substantial centrifugal forces, such as large fan clutches. A particular embodiment includes a magnetorheological fluid including a liquid, magnetizable particles, and a molybdenum-amine complex.

1. A magnetorheological fluid comprising:
 10 to 14 weight percent of a hydrocarbon-based liquid;  
 86 to 90 weight percent of bimodal magnetizable particles, wherein the bimodal magnetizable particles consist essentially of: 
 a first group of particles having a first range of diameter sizes with a first mean diameter having a standard deviation no greater than about two-thirds of the value of said mean diameter and  
 a second group of particles with a second range of diameter sizes and a second mean diameter having a standard deviation no greater than about two-thirds of said second mean diameter,  
 such that the major portion of all particle sizes fall within the range of one to 100 microns and the weight ratio of said first group to said second group is in the range of 0.1 to 0.9, and the ratio of said first mean diameter to said second mean diameter is five to ten;  
 
 0.05 to 0.5 weight percent fumed silica; and  
 0.5 to 5 weight percent, of the liquid mass, of a molybdenum-amine complex.  
 
     
     
       2. A fluid as recited in  claim 1  in which said particles comprise at least one of iron, nickel and cobalt. 
     
     
       3. A fluid as recited in  claim 1  in which said bimodal magnetizable particles comprise carbonyl iron particles having a mean diameter in the range of one to ten microns. 
     
     
       4. A fluid as set forth in  claim 1  wherein the first and second groups of particles are of the same composition. 
     
     
       5. A fluid as set forth in  claim 1  wherein the hydrocarbon-based liquid comprises a polyalphaolefin. 
     
     
       6. A fluid as set forth in  claim 1  wherein the hydrocarbon-based liquid comprises a homopolymer of 1-decene which is hydrogenated. 
     
     
       7. A magnetorheological fluid comprising:
 10 to 14 weight percent of a liquid phase comprising a polyalphaolefin;  
 86 to 90 weight percent of magnetizable particles, wherein the particles comprise carbonyl iron and consist essentially of: 
 a first group of particles having a first range of diameter sizes with a first mean diameter having a standard deviation no greater than about two-thirds of the value of said mean diameter and  
 a second group of particles with a second range of diameter sizes and a second mean diameter having a standard deviation no greater than about two-thirds of said second mean diameter,  
 such that the major portion of all particle sizes fall within the range of one to 100 microns and the weight ratio of said first group to said second group is in the range of 0.1 to 0.9, and the ratio of said first mean diameter to said second mean diameter is five to ten;  
 
 0.05 to 0.5 weight percent fumed silica; and  
 0.5 to 5 weight percent, of the liquid mass, of a molybdenum-amine complex.  
 
     
     
       8. A fluid as set forth in  claim 7  wherein the molecular weight of the polyalphaolefin ranges from about 280 to less than 300. 
     
     
       9. A magnetorheological fluid comprising:
 5 to 25 weight percent of a first liquid;  
 75 to 95 weight percent of magnetizable particles, wherein the magnetizable particles consist essentially of: 
 a first group of particles having a first range of diameter sizes with a first mean diameter having a standard deviation no greater than about two-thirds of the value of said first mean diameter and  
 a second group of particles with a second range of diameter sizes and a second mean diameter having a standard deviation no greater than about two-thirds of said second mean diameter,  
 such that the major portion of all particle sizes falls within the range of one to 100 microns and the weight ratio of each of said first group and said second group to the total weight of said magnetic particles is in the range of 0.1 to 0.9, and the ratio of said first mean diameter to said second mean diameter is five to ten; and  
 
 0.5 to 5 weight percent, of the liquid mass, of a molybdenum-amine complex.  
 
     
     
       10. A fluid as set forth in  claim 9  wherein the molybdenum-amine complex comprises 
                 
 
       wherein R is an alkyl group and x, y, and z are each independently selected from 1, 2, or 3. 
     
     
       11. A fluid as set forth in  claim 9  further comprising 0.05 to 0.5 weight percent fumed silica. 
     
     
       12. A fluid as set forth in  claim 9  wherein the first liquid comprises a polyalphaolefin. 
     
     
       13. A fluid as set forth in  claim 9  wherein the first fluid comprises a homopolymer of 1-decene which is hydrogenated. 
     
     
       14. A fluid as recited in  claim 9  in which said first and second groups of particles are of the same composition.